This invention relates in general to measuring radiant energy from a pulsed laser or light source and, in particular, to an instrument for automatically measuring the energy of each pulse received over a wide range of energy levels in the presence of high ambient light levels.
An instrument for reliably detecting laser pulses and measuring the pulse power levels in daylight must overcome several problems which complicate the process. Pulses of laser light may be of very short duration; in many applications, a typical pulse width is 10 to 20 nanoseconds or less. Laser pulses may have a wide range of energy levels. In daylight, the laser pulses may be present in sunlight having a much higher energy level than the laser pulses themselves. This ambient light level may also be modulated by atmospheric scintillations. Thus a laser pulse radiometer may be required to isolate and measure laser pulses of widely varying energy levels under varying ambient light conditions when fluctuations caused by atmospheric scintillations are present.
Conventional laser radiometers measure the peak voltage or current that the laser pulse produces in a detector to determine the pulse power. Changes in the radiometer gain are usually required for these instruments to accommodate laser pulses having a wide range of energy levels. An operator action may be required to manually switch the instrument range which increases the possibility that laser pulses having an energy outside of the present range will not be detected, or if detected, not accurately measured. An instrument which would automatically change to the proper range upon detection would be very complex and expensive. An operator is also usually required to adjust compensation circuitry for the ambient light level.
It is also desirable that a laser pulse radiometer, in addition to automatically detecting and measuring the power level of a laser pulse, have the capacity of automatically transmitting the data to data processing device for further use or storage.